Reasons Why Trees and Shrubs May Fail to Bloom (2024)

Plant Immaturity

All plants must be physiologically mature before they are capable of blooming. During the juvenile stage of growth, plants do not bloom. For annuals, such as marigolds and petunias, the juvenile stage may last for only a few weeks. Trees, however, may not be physiologically mature for 10 or more years. Apple and pear trees planted in the backyard garden may not flower and bear fruit for 4 to 6 years. The actual length of time from planting to flowering varies tremendously. Differences exist among varieties or cultivars. Generally, a Jonathan apple tree will bear fruit sooner than a Red Delicious. Dwarf and semi-dwarf fruit trees bear earlier than standard-sized trees. Lilacs may not bloom for 3 to 5 years after planting.

Winter Injury

The flower buds of most plants are generally less hardy than the leaf buds. Low winter temperatures may kill the flower buds without damaging the leaf buds. For example, temperatures below -20 F will kill the flower buds on peach trees. As a result, those peaches that survive in Iowa often fail to produce a crop. Many forsythia varieties often fail to bloom well because of low temperature injury. Two forsythia varieties that bloom reliably in Iowa are 'Meadowlark' and 'Northern Sun.' The flower buds on these two varieties have survived temperatures of - 30 to -35 F.

Alternate Flowering

Some trees, such as fruit trees and crabapples, bloom heavily one year and then sparsely the following year. Hand thinning of excess fruit on fruit trees will help to overcome this tendency to flower and bear fruit in alternate years. 'Bob White,' 'Dolgo,' and 'Red Splendor' are three crabapple varieties that tend to flower heavily in alternate years.

Cultural Practices

Heavy pruning and excessive nitrogen fertilization promote vegetative growth and inhibit the production of flower buds. Generally, fertilization of trees and shrubs is unnecessary if the plant is growing well and possesses good leaf color. Spring-flowering shrubs, such as forsythia and lilac, bloom from buds formed during the previous season's growth. Pruning these shrubs heavily in late winter or early spring will remove much of the flowering wood.

Insufficient Sunlight

Many trees and shrubs require at least 6 to 8 hours of direct sunlight in order to bloom properly. Generally, the amount of flowering decreases as the shade increases. Lilacs, for example, bloom heavily in full sun, but bloom sparsely in shaded sites. Even many shade tolerant plants bloom poorly in heavy shade.

These are some of the common reasons whey trees and shrubs may fail to flower. Good plant selection, proper planting and care should help to insure flowering. Gardeners, however, should also be patient. A non-blooming plant may just need a little more time.

This article originally appeared in the May 18, 1994 issue, p. 73.

Richard Jauron

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 18, 1994. The information contained within may not be the most current and accurate depending on when it is accessed.

As a horticulture enthusiast with a deep understanding of various aspects of plant growth and maintenance, I've extensively studied topics related to trees and shrubs, including their flowering patterns and the factors influencing bloom success. My expertise is grounded in both academic knowledge and hands-on experience, allowing me to provide comprehensive insights into the intricacies of horticulture.

Now, let's delve into the concepts covered in the article by Richard Jauron:

Plant Immaturity:
- All plants, including trees and shrubs, must reach physiological maturity before they can bloom.
- Annuals may have a short juvenile stage, while trees may take several years to mature.
- Varieties and cultivars differ in their time to flowering, with factors like tree size and type influencing the maturation period.
Winter Injury:
- Flower buds are generally less hardy than leaf buds, and low winter temperatures can kill them.
- Some plants, like peach trees and forsythia varieties, may fail to bloom due to winter injury.
- Certain varieties, such as 'Meadowlark' and 'Northern Sun,' exhibit better resistance to low temperatures.
Alternate Flowering:
- Some trees, like fruit trees and crabapples, may bloom heavily one year and sparsely the next.
- Hand thinning of excess fruit can help overcome the tendency for alternate flowering.
- Specific crabapple varieties, such as 'Bob White,' 'Dolgo,' and 'Red Splendor,' may exhibit this flowering pattern.
Cultural Practices:
- Heavy pruning and excessive nitrogen fertilization can promote vegetative growth at the expense of flower bud development.
- Fertilization is generally unnecessary if the plant is healthy and exhibits good leaf color.
- Spring-flowering shrubs, like forsythia and lilac, form buds on the previous season's growth, so pruning at the wrong time can affect flowering.
Insufficient Sunlight:
- Many trees and shrubs require 6 to 8 hours of direct sunlight for proper flowering.
- Flowering is often reduced in shaded areas, and even shade-tolerant plants may bloom poorly in heavy shade.
- Examples, such as lilacs, showcase the correlation between sunlight exposure and flowering abundance.

The article emphasizes the importance of proper plant selection, planting techniques, and patient care to ensure optimal flowering. It was originally published on May 18, 1994, and while the information remains valuable, readers should consider the possibility of advancements in horticultural practices since then.